Recently, mobile communication standards are stressing Quality of Service (QoS) to assure traffic rate and latency required in an application, QoS differentiation on a user profile basis, and service parameters defined in connection admission. In a mobile communication system, the QoS is guaranteed in association with various schemes such as Connection Admission Control (CAC) for determining whether to admit the connection, flow control (e.g., leaky bucket) for controlling a source traffic rate in accordance with a network condition, and packet scheduling for controlling usage of radio channels between a base station and a terminal, by referring to QoS parameters from a user and the network condition.
Particularly, the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard provides quite detailed and sub-divided features in the QoS definition and differentiation. For example, the IEEE 802.16 standard defines QoS parameters of a minimum reserved traffic rate and a maximum sustained traffic rate. Also, the IEEE 802.16 standard supports Unsolicited Grant Service (UGS), real-time Polling Services (rtPS), and non-real-time Polling Services (nrtPS).
The minimum reserved traffic rate is used to meet a minimum traffic rate required in the application of real time service, or to keep a packet transmission interval of non-real-time service below a certain interval. The UGS connection of the IEEE 802.16 standard periodically allocates slots for the minimum reserved traffic rate in an unsolicited pattern. Accordingly, there are no more subjects to be considered to meet the minimum reserved traffic rate in the UGS connection. In the rtPS connection of the IEEE 802.16 standard, statistically, it is highly likely to satisfy the minimum traffic rate through the CAC. The application frequently using the rtPS connection is a video streaming service. The video streaming generates burst traffic at a video codec at intervals. Hence, the minimum traffic rate can be fully satisfied when the chance to select is guaranteed by acquiring several tokens at intervals. The nrtPS connection of the IEEE 802.16 standard, which has no required latency, exhibits the traffic rate in proportion to the channel condition. This is scheduled by a packet scheduler (e.g., a proportional fair scheduler). To raise the possibility of the traffic rate satisfaction, the packet scheduler multiplies by a weighting factor greater than 1 when calculating the priority. When the multiplied weighting factor is too great, the wireless bandwidth is monopolized. Thus, the traffic rate becomes too high and it may be problematic in view of the fairness. By contrast, when the multiplied weighting factor is too small, there would be not enough chances to select meet the minimum reserved traffic rate. Therefore, to effectively meet the minimum reserved traffic rate in the nrtPS connection, a method for determining an adequate weighting factor is required.
The maximum sustained traffic rate is used to provide the QoS based on a level of a subscriber. When the limited bandwidth is fairly allocated to the subscribers, the subscriber of the better channel condition acquires the higher traffic rate. When the traffic rate allocated to the subscriber is restricted, it is possible to allocate the small bandwidth to the subscriber who pays smaller fee in the good channel condition and then to allocate the remaining bandwidth to the subscriber who requires the high traffic rate and pays the considerable fee. That is, the subscriber requiring the high QoS acquires the high maximum sustained traffic rate while paying the considerable fee. Yet, the maximum sustained traffic rate is used to limit the traffic rate in accordance with the paid fee, rather than to guarantee the traffic rate.
Therefore, what are needed are an apparatus and a method for guaranteeing the minimum reserved traffic rate and the maximum sustained traffic rate in the non-real-time service of the mobile communication system.